The assignee of the present invention manufactures and deploys spacecraft for, inter alia, communications and broadcast services. Market demands for such spacecraft have imposed increasingly stringent requirements on spacecraft payloads. For example, broadband service providers desire spacecraft with increased data rate capacity at higher EIRP through each of an increased number of user spot beans operable from geosynchronous orbit altitudes in communication with small (<1 meter aperture) user terminals.
A multi-beam antenna (MBA) system generates a set of user spot beams that define a coverage area which may extend, in aggregate, across a large region on the ground. MBAs providing wide-band communications services from a geosynchronous satellite conventionally provide contiguous coverage of a region with a triangular lattice of overlapping circular antenna beams. These beams are conventionally formed using clusters of radiating elements configured as circular feed horns, also centered on a triangular lattice.
An objective of an MBA system is to maximize beam forming efficiency, measured as gain area product (GAP) of the MBA divided by 4π steradians (41,253 square degrees). GAP=Gave*Acov, where Gave is the average gain over coverage area, Acov, with Acov, expressed in square degrees. Known MBA systems provide a GAP of 10000-16000 and, therefore, a beam forming efficiency in the range of 24% to 39%. See: Han, C. C., et al., “Satellite Antennas”, Antenna Handbook, volume 3, chapter 21, edited by Lo, Y. T., et al., ISBN 0-442-01594-1 (hereinafter, “Han”), the disclosure of which is hereby incorporated by reference.
In the absence of the presently disclosed techniques, a single aperture, array fed reflector MBA may share radiating elements between two or more beams, complicating the beamforming and requiring multi-carrier operation. Multi-carrier operation requires linearity which leads to output back-off of the amplifiers and reduced amplifier efficiency with increased power and heat generated for a given output power. Alternatively, an arrangement having a single feed horn per beam with a conventional multi-reflector MBA requires higher power amplifiers and amplifier redundancy, with increased cost and complexity. Moreover, an MBA having a single feed per beam is generally scan limited by reflector offset distortion.
Thus, an improved single aperture MBA design is desirable.